The invention relates to a system and clamp for supporting a load in the event of failure of the normal supporting structure between the clamp and the load.
For construction and other purposes, it is often useful to raise a load by means of a cable attached to a cage or some other load supporting structure. Particularly in a life supporting system in which personnel ride in the cage, it is desirable to provide some back-up system which will support the load in the event of failure of the cable or the attachment of the cable to the personnel cage. Such a failure can be due to errors of installing a main clamp, faulty materials, fatigue of the clamp or the cable, or damage to the cable caused by the main termination. Cable fatigue in particular happens almost always within three feet of the main termination.
According to the present invention, a clamp is provided on the cable above the point of attachment to the load supporting structure. The clamp includes first and second members having opposed curved surfaces defining therebetween an extending passage for the cable. One of the members is mounted for movement toward and away from the cable, for example, in a U-shaped channel provided by another member. A cam member is mounted outward from the cable for pivotable movement about an axis in a vertical plane. The cam member engages the one member which is movable toward and away from the cable, and also includes structure for attaching the cam member to the load remote from the axis of rotation, for example, by a chain. Failure of the cable or attachment thus causes the cam member to pivot about its axis, so that its surface applies an increasing force to the one member to frictionally lock the clamp to the cable and support the load.
The present invention has a number of advantages. It can be made of readily available materials such as steel, and is simple in construction. Its installation is simple, and it does not restrain the working of the cable. It does not preload the clamp or restrain the cable until failure and it lends itself to visual inspection. Readily available materials can be used to fabricate the clamp in a normal machine and fabricating shop. Location of the back-up clamp can be such that it will protect against almost all foreseeable failures.
Others in the past have sought to provide automatic safety catches. For example, the U.S. patent to Wallace No. 1,002,947, and the U.S. patent to Metheen No. 1,080,648, both show safety catch structure for elevators in which a wedge is used to lock the elevator to the cable in the event of failure. The present invention utilizes both friction and leverage with the advantages described above. The U.S. patent to Eck No. 498,161 describes eccentric cams which engage a safety cable and the U.S. Pat. to Wakefield No. 473,275 describes an elevator which may be secured for loading by a pair of tooth dogs. Other U.S. patents showing clamping to ropes include the patent to DeWit No. 92,837, the patent to Wilson No. 1,334,925, the patent to Hecker No. 1,947,603, the patent to Swager No. 4,077,094, the patent to Hubert No. 2,993,157, the patent to Thompson No. 3,386,530, and the patent to Christiensen No. 3,967,349.
Other objects and purposes of the invention will be clear from the following detailed description of the drawings.